LMC6772AIM NSC [National Semiconductor], LMC6772AIM Datasheet - Page 7

• Manufacturer Part Number: LMC6772AIM
• Description: Dual Micropower Rail-To-Rail Input CMOS Comparator with Open Drain Output
• Manufacturer: NSC [National Semiconductor]

1.0 Input Common-Mode Voltage
Range
LMC6772 can compare the sensor signal with an appropri-
ately small reference voltage. This reference voltage can be
close to ground or the positive supply rail.
2.0 Low Voltage Operation
Comparators are the common devices by which analog sig-
nals interface with digital circuits. The LMC6772 has been
designed to operate at supply voltages of 2.7V, without sac-
rificing performance, to meet the demands of 3V digital sys-
tems.
At supply voltages of 2.7V, the common-mode voltage range
extends 200 mV (guaranteed) below the negative supply.
This feature, in addition to the comparator being able to
sense signals near the positive rail, is extremely useful in low
voltage applications.
At V
4 µs with overdrives of 100 mV. Please refer to the perfor-
mance curves for more extensive characterization.
3.0 Output Short Circuit Current
The LMC6772 has short circuit protection of 40 mA. How-
ever, it is not designed to withstand continuous short circuits,
transient voltage or current spikes, or shorts to any voltage
beyond the supplies. A resistor is series with the output
should reduce the effect of shorts. For outputs which send
signals off PC boards additional protection devices, such as
diodes to the supply rails, and varistors may be used.
4.0 Hysteresis
If the input signal is very noisy, the comparator output might
trip several times as the input signal repeatedly passes
through the threshold. This problem can be addressed by
making use of hysteresis as shown below.
FIGURE 2. Even at Low-Supply Voltage of 2.7V, an
Input Signal which Exceeds the Supply Voltages
+
= 2.7V, propagation delays are t
Produces No Phase Inversion at the Output
(Continued)
PLH
= 4 µs and t
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PHL
=
7
The capacitor added across the feedback resistor increases
the switching speed and provides more short term hyster-
esis. This can result in greater noise immunity for the circuit.
5.0 Spice Macromodel
A Spice Macromodel is available for the LMC6772. The
model includes a simulation of:
and many more characteristics as listed on the macromodel
disk.
Contact the National Semiconductor Customer Response
Center at 1-800-272-9959 to obtain an operational amplifier
spice model library disk.
Typical Applications
Universal Logic Level Shifter
The output of the LMC6772 is the uncommitted drain of the
output NMOS transistor. Many drains can be tied together to
provide an output OR’ing function. An output pullup resistor
can be connected to any available power supply voltage
within the permitted power supply range.
The two 1 k
supply voltage. The pull-up resistor should go to the output
logic supply. Due to its wide operating range, the LMC6772
is ideal for the logic level shifting applications.
• Input common-mode voltage range
• Quiescent and dynamic supply current
• Input overdrive characteristics
FIGURE 3. Canceling the Effect of Input Capacitance
FIGURE 4. Universal Logic Level Shifter
resistors bias the input to half of the power
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www.national.com
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